Add tests for transform function

__tests__/__snapshots__/transform.test.js.snap

@@ -0,0 +1,21 @@
+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`transform basic 1`] = `
+"module.exports = {
+  plugins: [\\"@babel/plugin-transform-classes\\", \\"@babel/plugin-syntax-jsx\\"],
+  presets: [\\"@babel/preset-env\\"]
+};
+"
+`;
+
+exports[`transform function 1`] = `
+"function createBabelrc() {
+  return {
+    plugins: [\\"@babel/plugin-transform-classes\\", \\"@babel/plugin-syntax-jsx\\"],
+    presets: [\\"@babel/preset-env\\"]
+  };
+}
+
+module.exports = createBabelrc();
+"
+`;

__tests__/transform.test.js

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+const fs = require('fs');
+const path = require('path');
+const pify = require('pify');
+const transform = require('../src/transform');
+
+async function readFile(configPath) {
+  return (await pify(fs.readFile)(path.join(__dirname, configPath), 'utf8'));
+}
+
+describe('transform', () => {
+  test('basic', async () => {
+    const src = await readFile('../fixtures/transform/basic.js');
+    expect(transform(src)).toMatchSnapshot();
+  });
+
+  test('function', async () => {
+    const src = await readFile('../fixtures/transform/function.js');
+    expect(transform(src)).toMatchSnapshot();
+  });
+});

fixtures/transform/basic.js

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+module.exports = {
+  plugins: ['babel-plugin-transform-es2015-classes', 'babel-plugin-syntax-jsx'],
+  presets: ['babel-preset-env']
+};

fixtures/transform/function.js

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+function createBabelrc() {
+  return {
+    plugins: ['babel-plugin-transform-es2015-classes', 'babel-plugin-syntax-jsx'],
+    presets: ['babel-preset-env']
+  };
+}
+
+module.exports = createBabelrc();